In a magnetohydrodynamic (MHD) power generation plant a fuel such as coal is burned at a very high temperature to provide a rapidly moving stream of hot ionized gas. The ionized gas passes between magnets which induces a current in electrodes on either side of the stream of gas. In order to increase the efficiency of the process, a seed such as potassium carbonate is injected into the gas stream to increase its conductivity. The use of potassium carbonate has the additional advantage of scavenging sulfur in the gas to form potassium sulfate, thereby removing a potential pollutant from the exhaust gases.
Because potassium carbonate is expensive and large quantities of it must be used, it is necessary to recover the potassium sulfate and convert it back into potassium carbonate for reuse in the MHD power plant. One process for doing this is the Argonne National Laboratory process, which has two steps. In the first step the potassium sulfate and oil are reacted to produce potassium sulfide and carbon dioxide. In the second step the potassium sulfide is reacted with water and carbon dioxide to produce potassium carbonate and hydrogen sulfide. This second step is an all-wet process because the water used is a liquid. Because liquid water is used, energy must be expended to thoroughly dry out the resulting potassium carbonate salt because the hydrogen present in water uses up electrons in the hot ionized gas and reduces the efficiency of the MHD generation process.
Another process for converting potassium sulfate to potassium carbonate is known as the PERC process. In the PERC process the potassium sulfate is reacted with hydrogen and carbon monoxide to produce potassium sulfide, water, and carbon dioxide. In the second step the potassium sulfide is reacted with water and carbon dioxide to produce potassium carbonate and hydrogen sulfide. The first step in the PERC process is expensive because the generation of the hydrogen and carbon monoxide is expensive. Also, the first reaction is very slow because the potassium sulfate is a solid and the gases that react with it must diffuse into it.